The art of managing metallic ions in food products has received much attention by the food industry. Metallic ions of iron, copper and zinc can be present in some food products with adverse effects on food integrity. If they are allowed to remain in some food products even in low concentrations, such metallic ions can greatly reduce the shelf life of some fats, oils and other foods greatly reduce the shelf life of some fats, oils and other foods that are subject to spoiling and oxidization.
Sequestrants are chemicals that deactivate or stabilize these metallic ions by chemically tying up the metal ions through chemical reactions to form stable complexes that do not adversely affect the integrity or quality of such food products. Sequestrants are also known as sequestering agents, stabilizers, chelators, chelating agents and metal scavengers. Sequestrants help to establish, maintain, and enhance the integrity of many food products. From a food manufacturing viewpoint, sequestrants serve to stabilize or enhance the numerous properties identified with wholesome food including color, flavor and texture. Usually, sequestrants chemically react with metallic ions to form complexes which, depending on the stability of the metal complex, tend to alter the properties and effects of the metal in a substrate. Many sequestrants employed in food production occur naturally in nature. They include as monocarboxylic acids gluconic and acetic acids which weakly sequester zinc ions; as hydroxycarboxylic acids citric and tartaric acids which may sequester zinc ions; as amino acids such as sweet tasting lysine, glycine, leucine, alanine, and valine which may sequester zinc ions; and various macromolecules such as porphyins, peptides and proteins. Certain commercial sweeteners such as saccharin, sorbitol, mannitol and a constituent of aspartame, phenylalanine, have also been shown to bind with or sequester certain metals. For sequestration, chelation, to occur two general conditions must be met: (a) the ligand must have the proper steric and electronic configuration in relation to the metal ion being complexed and (b) the surrounding milieu (pH, ionic strength, solubility, etc) must likewise be conducive to complex formation. That sequestration of metal ions is a desirable goal of food manufacturers is well known in the art. Sequestration in food is reviewed and referenced in CRC Handbook of Food Additives, 2nd Ed. 1972. Stability constants are exhaustively compiled in Stability Constants of Metal-Ion Complexes and its supplement which are special publications 17 and 25 of The Chemical Society published by Burlington House, London in 1964 and 1968.
However, the desirability of sequestering metal ions in all cases must be challenged in view of the nature of some metal chelators relative to the environment in which their use is intended. For example, the use of zinc gluconate lozenges and similar means has been described as a method for reducing the duration of common cold symptoms (U.S. Pat. No. 4,503,070, Mar. 5, 1985 and any reissues and continuations-in-part). In such usage, zinc ions are only weakly bound by the gluconate moiety. Judging from the stability constant of zinc gluconate, log K.sub.1 1.70, nearly all zinc appears to be ionized in solution with water from saliva at any given time. Such ions appear available for those biochemical activities in the oral and oral pharyngeal mucous membranes that result in a reduction in the duration of common cold symptoms. Although the exact nature of the biochemical activity of zinc ions in reducing the duration of common cold symptoms remains to be determined, it appears that the zinc complex must be ionizable. Published articles, "Reduction in Duration of Common Cold Symptoms by Zinc Gluconate Lozenges in a Double Blind Study", Antimicrobial Agents and Chemotherapy, 1984, 25(1), pp20-24 by George A. Eby, et al; and "Prophylaxis and Treatment of Rhinovirus Colds with Zinc Gluconate Lozenges", Journal of Antimicrobial Chemotherapy, 1987, 20(6), pp 893-901 by W. Al-Nakib, et al, both use zinc gluconate with no additional metal sequestrants added and both showed a marked reduction in the duration of common cold symptoms.
Conversely, in a similar study "Two Randomized Controlled Trials of Zinc Gluconate Lozenge Therapy of Experimentally Induced Rhinovirus Colds", Antimicrobial Agents and Chemotherapy, 1987 31(8) pp 1183-1187, by Jack M. Gwaltney, Jr. et al, citric acid, a very strong zinc chelator, was used in the lozenges in large amounts which were sufficient to eliminate the taste of zinc, resulting in no reduction in the duration of the common cold. The stability constant of citric acid for zinc ions is generally accepted to be log K.sub.1 4.5. In oral use in lozenge form, zinc gluconate rapidly ionizes; as does zinc combined with other ligands having low stability constants. It is known in the art that if such occurs in the presence of sufficient amount of an acid having a high stability constants for zinc ions such as equimolar (or greater) citric acid, a new, vastly stronger equilibrium may occur. Such equilibrium may result in stable compounds having little or no bioavailabilty at normal pH as would be found in saliva. In the case of lozenges containing zinc gluconate with citric acid, soluble zinc complexes were shown to be tasteless and were proposed to be sufficiently biologically available to be effective in reducing the duration of common colds. However, with addition of sufficient citric acid, there occurs in saliva such powerful binding of zinc ions, that there is no metallic taste observed; no localized activity and no observable efficacy in reducing the duration of common colds.
In as much as there is an important need to develop pleasant tasting lozenges and other means of introducing zinc ions to the oral and oral pharyngeal mucous membranes for the treatment of common colds; and in as much as serious mistakes taken from the prior art of taste management of zinc and other metallic ions have been made, particularly in the taste management of zinc lozenges; it is apparent that the errors of the prior art receive attention and a new way of eliminating the taste and aftertaste of ionizable zinc compounds be developed.